Count cache access and hits in InMemoryCache and Redis cache

Hello @ArtemTitoulenko, @don-neufeld, 

Please review the following commits I made in branch 'xiao-monitor-hit-miss'.

f30c3a8c692dddf8c4ee4f62af67026e57414fd5 (2013-08-05 12:26:34 -0700)
Count cache access and hits in InMemoryCache and Redis cache


R=@ArtemTitoulenko
R=@don-neufeld